P3 Interactions — Magnets 🧲
Created by Miss Clarissa Ng | www.clartutors.com
🧲 Types of Magnets
- Naturally-occurring magnets are known as lodestones.
- Magnets can be made of iron or steel. They come in many shapes and sizes.
- Some examples are bar magnets, U-shaped magnets and ring magnets.
⚡ Properties of Magnets
- Magnets attract objects made of magnetic materials.
- Magnets exert a magnetic force of attraction on magnetic materials, such as iron and steel.
- Other materials, such as wood, plastic, glass, aluminium and copper, are not attracted to magnets and are known as non-magnetic materials.
💪 Magnetic Strength
- The poles of a magnet have the greatest magnetic strength.
- Bar magnet — poles are at the ends.
- Ring magnet — poles are at the top and bottom surfaces.
The poles of a bar magnet are at the ends of the magnet.
🔄 Attraction and Repulsion
- Unlike poles of magnets attract, while like poles repel.
- Every magnet has two poles: the north-seeking pole and the south-seeking pole.
- Magnets can interact with one another by either attracting (pulling) or repelling (pushing) each other.
- When the unlike poles of two magnets are facing each other (N - S), the two magnets will attract and move towards each other.
- When the like poles of two magnets are facing each other (N - N or S - S), the two magnets will repel and move away from each other.
📝 Common Question: Arrangements of magnets
The diagram below shows the arrangements of three bar magnets.
Not possible (N-N repel)
Possible (unlike poles attract)
- Arrangement A is not possible as the like poles of two magnets (N - N) are facing each other. Hence the magnets would repel.
- Arrangement B is possible as the unlike poles of two magnets are facing each other. Hence the magnets would attract.
Investigating if an object is a magnet, made of a non-magnetic material or made of a magnetic material
The observations are recorded in the table below.
| Metal bar | Observations (North-seeking pole and X) | Observations (North-seeking pole and Y) |
|---|---|---|
| A | Did not move | Did not move |
| B | X moved away from the magnet | Y moved towards the magnet |
| C | X moved towards the magnet | Y moved towards the magnet |
- Both ends of Metal bar A did not move, indicating that they were neither attracted to nor repelled by the bar magnet. Hence, Metal bar A is made of a non-magnetic material.
- End X of Metal bar B moved away from the north-seeking pole of the magnet, indicating that they repelled each other. Since only magnets can repel another magnet when their like poles face each other, Metal bar B must be a magnet.
- Both ends of Metal bar C moved towards the magnet, indicating that both ends were attracted to the magnet. Hence, Metal bar C is made of a magnetic material.
⚖️ Comparing the Magnetic Strength of Magnets
- The size of a magnet does not affect its magnetic strength.
- Different magnets have different magnetic strengths. In order to find out and compare the magnetic strength of different magnets, various experiments can be carried out.
Method 1: Comparing the number of magnetic objects attracted to each magnet
The greater the number of magnetic objects a magnet can attract, the greater the magnetic strength of the magnet.
In the diagram above, Magnet X has a greater magnetic strength than Magnet Y as Magnet X attracted more paperclips than Magnet Y from the same height above the paperclips.
Method 2: Comparing the distance from which each magnet can attract a magnetic object
The greater the distance from which a magnet can attract an object, the greater the magnetic strength of the magnet.
In the diagram above, Magnet W has a greater magnetic strength than Magnet Z as the same number of paperclips were attracted to Magnet W from a greater distance.
Method 3: Comparing the total mass of the magnetic objects the magnets can attract
The greater the total mass of the magnetic objects a magnet can attract, the greater the magnetic strength of the magnet.
In the diagram above, Magnet B has a greater magnetic strength than Magnet A as Magnet B attracted a greater mass of nails than Magnet A.
🔧 Making a Temporary Magnet
The Stroke Method
- An object made of a magnetic material, such as iron or steel, can be magnetised by stroking its entire length several times with the same pole of a magnet in one direction.
- The end of the object where the pole of the magnet first touches will be the same polarity as the pole of the magnet.
Factors that affect magnetic strength
- The greater the number of strokes along the magnetic object, the greater the magnetic strength of the temporary magnet.
- The greater the magnetic strength of the permanent magnet used to stroke the magnetic object, the greater the magnetic strength of the temporary magnet.
The Electrical Method
- An object made of magnetic material, such as iron or steel, becomes magnetised when it is placed inside a coil of wire and an electric current is passed through the coil.
- This type of magnet is called an electromagnet.
Factors that affect magnetic strength
- The greater the number of coils of wire around the magnetic object, the greater the magnetic strength of the electromagnet.
- The greater the number of batteries used, the greater the magnetic strength of the electromagnet.
🔥 Losing Magnetic Strength
A magnet can lose its magnetic strength when it is:
- Heated over a strong flame
- Dropped repeatedly
- Hammered repeatedly
📝 Exam Tip
Remember:
- Magnetic materials: Iron, steel (attracted to magnets)
- Non-magnetic materials: Wood, plastic, glass, aluminium, copper (not attracted to magnets)
- Unlike poles attract (N-S), like poles repel (N-N or S-S)
- Only magnets can repel another magnet when their like poles face each other — magnetic materials are always attracted
- A freely suspended or a freely floating magnet will always come to rest in the North-South direction
📋 Summary Table
| Key Concept | Description |
|---|---|
| Magnetic materials | Materials attracted to magnets (iron, steel) |
| Non-magnetic materials | Materials not attracted to magnets (wood, plastic, glass, aluminium, copper) |
| Magnetic force of attraction | The force that pulls magnetic materials towards a magnet |
| Unlike poles attract | North-seeking pole and south-seeking pole pull towards each other (N-S) |
| Like poles repel | Same poles push away from each other (N-N or S-S) |
| Magnetic strength | Greatest at the poles of a magnet; can be compared by number of objects attracted, distance, or total mass |
| Temporary magnet | Made by stroking a magnetic material with a permanent magnet; strength increases with more strokes and stronger magnets |